The invention relates to testing of high-speed systems. More particularly, the invention relates to a test package for accurate testing of high-speed systems.
The performance of a system is dependent on the performance and characteristics of each of the individual components within the system and the signal paths connecting the components. A system can only run as fast as its slowest link. In designing and testing a system to meet performance criteria, it is important to ensure that each component and path of the system is able to meet or exceed the performance requirements.
A given system may need to operate at certain frequencies, and, in order to do so, each component and path in the system must also be capable of supporting those frequencies. Modern systems must run at ever-increasing frequencies, and as the speed of these systems increase, guaranteeing error-free performance at speed becomes more and more critical. At multi-gigabit speeds and beyond, a very small timing error can have enormous consequences and cause fatal errors.
In order to meet performance requirements, the components and paths in a system are designed carefully to ensure that they meet the specific performance targets. These parts are usually simulated during the design phase, and then, after fabrication or manufacturing, tested for their performance characteristics. It is important to be able to understand and characterize the performance of the part as accurately as possible.
One component of a system can be the printed circuit board (PCB). A system may have several such circuit boards, each having one or more integrated circuits (ICs) and other components mounted on it, which are connected by traces. A trace is a conducting path on a PCB which can carry a signal. In modern high-speed systems, insertion loss and off-chip loading from the traces often dominates the overall performance of the system. The parasitic effects, that is resistance, capacitance, and inductance, presented by the traces on the circuit board can be orders of magnitude greater than those found inside an IC. Therefore, the ability to measure and characterize accurately the effects of these traces can be very important.
Simulation of the traces is usually based on a behavioral model which is developed using empirical data. Accuracy of a simulation depends on many factors, including the accuracy of the model, and the computing power and time available. For high-speed systems, simulation may only offer a rough estimate of the behavior of the trace, and lacks the precision necessary for modern systems. As speeds continue to increase and models become more complex and less accurate, simulation may not be practical.
After manufacturing, a trace may be tested by connecting a probe to a circuit board. This may be done with none, some, or all of the ICs and other components mounted on the board. A small xe2x80x9cstub,xe2x80x9d which is a short partial trace attached to the main trace, may be provided so that a probe may be connected to that point. However, even when the stub is very close to the endpoint of the trace (where a signal starts or ends), there are inaccuracies because the measurement point is not at the exact endpoint. Measurements taken from a probe connected to a stub may include erroneous data caused by reflections from the real endpoint, the effects of the stub itself, interference from IC switching activity, or other factors.
Probes may also be attached elsewhere, but ultimately, accurate measurement is limited by the placement of the probes. Any probe that is not attached in exactly the same place and manner as the component or path being tested will necessarily introduce inaccuracies in measurement. Therefore, a need exists for a way to test a component or path of a system with a high degree of accuracy by testing at the actual point of interest.
in accordance with the present invention, a test package with a connector that allows for an external connection to be made is placed in a system for testing. The package is designed in such a way as to allow the user to test conducting paths in the system with a very high degree of accuracy under conditions which closely mimic actual operating conditions.
In accordance with another embodiment of the present invention, a method for testing comprises placing a test package in a system and connecting an external tester to the test package. The external tester can then be used to send or receive signals to and from conducting paths in the system through the test package.